I switched from AC 70s and ac110s to emp 400s and never looked back so far. Just sold of my last crappy AC110!
Love the emp 400s, the biowheels will never get stuck if you clean the filter about every 6 months. There are spray bars in the emp 400s to make sure the biowheels do not get stuck. I own 4 of these filters and love them since you can put whatever you want in them. I use the sponges that come with them and put matrix in the grey cartridge things. I also put pothos in front of the sponges to take up nitrates without having to worry about the roots touching the impeller.
Nothing wrong with the ACs really unless one breaks and floods your apartment and you almost get kicked out of your apartment and the Hagen Company refuses to answer your emails or send you any parts (can you tell this is personal experience here?). Also the Acs are a little noisy for my liking, I like quiet in my bedroom.
That would be the main reason why I switched from ACs to marineland filters. I do also use Rena Canisters as well with my Marinelands.
As for quality going down hill on them, I honestly don't know. I did have a few that arrived broken, but marineland sent me brand new ones (only took a few days) and told me to keep the old ones for spare parts. It was great and the best customer service I have ever dealt with.
Best of luck with whatever you choose. I do think Emp 400s are one of the most underrated HOB filters. They are certainly my favorite HOB filter.